Probably the simplest, reversible drive circuit is the H-Bridge. Some BEAMbots use H-bridge motor drivers; many more use an H-bridge variant of some sort. Here's a simple conceptual schematic: Image Based on the SN74LS194 - Bidirectional Universal Shift Register the circuit is designed to drive UNIPOLAR type stepper motors and provides only basic control functions - Forward, Reverse, Stop and Speed adjustment. The only step angle for this driver is the design step angle for the motor. The circuit is not complex and is cheaper than many dedicated driver/controller devices and the parts are easy to find.

Build your own LC Meter and start making your own coils and inductors. This LC Meter allows to measure incredibly small inductances making it perfect tool for making all types of RF coils. LC Meter can measure inductances starting from 10nH - 1000nH, 1uH - 1000uH, 1mH - 100mH and capacitances from 0.1pF up to 900nF. The circuit includes an auto ranging and "Zero Out" function to make sure the readings are as accurate as possible ... [more]